In recent years, as a projection optical system which is used for a projector and by which a large screen can be obtained by projecting an image from a short distance, a projection optical system in which a refraction optical system and a concave mirror are used is suggested (for example, see PTL 1 and PTL 2).
However, for example, in PTL 1 (JP-A-2006-235516), although a very wide viewing angle is implemented using the refraction optical system and the concave mirror, the curved mirror is very large and the entire length thereof is very long. In PTL 2 (JP-A-2007-079524), for example, a mirror size is made small by combining a concave mirror and a convex mirror while setting the viewing angle to approximately 60 degrees in an eighth example. However, similar to PTL 1 described above, the entire length is very long. Configured two mirrors are aspherical mirrors and it is very difficult to manufacture the mirrors from a viewpoint of accuracy and assembly.
As described above, in a composite optical system including the refraction optical system and the concave mirror, an ultra-wide viewing angle is obtained while it is difficult to make the entire length small. For that reason, the composite optical system is not fit for, for example, a device that places importance on portability like a front projector.